1. Technical Field of the Invention
The present invention relates generally to an optical scanner which may be used in a laser scanning bar code reader or a laser scanning obstacle detector for automotive vehicles, and more particularly to an improved vibration-resisting structure of an optical scanner capable of scanning a given range accurately free from vibrational disturbances and a two-dimensional scanning device using the same.
2. Background Art
Japanese Patent First Publication No. teaches a low-cost optical scanner for use in emitting a laser beam in a bar coder reader or an obstacle detector. This scanner has a mirror-finished magnet supported by a torsion spring and subjects the magnet to an alternating field to move the magnet in a direction in which the torsion spring is twisted so that light from a source is reflected on the magnet to scan a target.
In the above scanner, increasing a scan angle requires decreasing the diameter of the torsion spring to 140 xcexcm to increase the degree of elastic deformation thereof. This, however, encounters the drawback in that the torsion spring is extended or bent easily in a direction different from a twisted direction required for a scanning operation. In other words, the magnet supported by the torsion spring undesirably undergoes vibrations in various directions different from the twisted direction required for the scanning operation. Thus, in a case where the scanner is installed in an automotive vehicle for obstacle detection, strong acceleration-caused vibrational disturbances act on the magnet, thereby resulting in undesirable deflection of a scanning beam.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an optical scanner designed to keep the deflection of a scanning beam to a minimum even when the scanner undergoes vibrational disturbances in various directions and a two-dimensional scanning system using the same.
According to one aspect of the invention, there is provided an optical scanner which may be employed in a laser beam bar code reader or an automotive obstacle detector equipped with a radar. The optical scanner comprises: (a) a housing; (b) a scanning mechanism constructed to be swingable about a given swing line to emit a light beam for scanning a given angular range, the scanning mechanism including a base and an inertia body projecting from the base toward the given swing line; (c) a support supporting the scanning mechanism on the housing so as to allow the scanning mechanism to swing, the support including a plurality of elastic plates each having a length one end of which is attached to the housing and other end of which is attached to the base of the scanning mechanism so that the elastic plates intersect each other with an offset on a line parallel to the given swing line, each of the elastic plates having a width in a direction parallel to the given swing line; and (d) a driver swinging the scanning mechanism to direct the light beam to the given angular range.
In the preferred mode of the invention, the inertia body is so provided that the center of gravity of the scanning mechanism is defined on the given swing line.
The inertia body may include a gravity center location adjusting mechanism capable of adjusting a location of the center of gravity of the scanning mechanism.
The base of the scanning mechanism has formed thereon a reflecting surface for reflecting the light beam emitted from a light source toward the given angular range.
The base of the scanning mechanism may have a mount extension plastically bent from at least one of ends thereof opposed in a direction parallel to the given swing line. The inertia body is mounted on the mount extension.
The mount extension may have a holder in which the inertia body is press fit.
The elastic plates have the same length between the housing and the scanning mechanism.
The elastic plates may be implemented by a first hollow rectangular spring plate and a second hollow rectangular spring plate. The second hollow rectangular plate passes through an opening of the first hollow rectangular plate so as to intersect the first hollow rectangular plate with the offset on the line parallel to the given swing line.
The elastic plates may alternatively be implemented by a first and a second U-shaped spring plate each including a base portion and a pair of arms extending from the base portion at an interval away from each other. The interval is greater than a width of the arms. One of the arms of the first U-shaped spring plate passes between the arms of the second U-shaped spring plate.
Each of the elastic plates may have rigidity resistant to change in form thereof which increases as approaching a portion of the elastic plate joined to the housing from a portion of the elastic plate joined to the scanning mechanism. This may be achieved by increasing the width of each of the elastic plates toward the housing.
Each of the elastic plate has the ends press fit in portions of the housing and the scanning mechanism, respectively.
Each of the housing and the scanning mechanism has ends opposed in a direction perpendicular to the given swing line. Each of the ends is bent to hold a corresponding one of the ends of the elastic plates tightly to join the housing and the scanning mechanism together.
Each of the elastic plates is joined to the housing and the scanning mechanism while undergoing elastic deformation.
Each of the elastic plates may have clips which are fitted on the end of the housing and the end of the scanning mechanism to join the housing and the scanning mechanism together.
Each of the housing and the scanning mechanism may have connecting portions each of which is connected to one of the ends of the elastic plates. Either of the connecting portions and the ends of the elastic plates has a protrusion, and the other has an engaging portion engaging the protrusion for securing a positional relation therebetween.
The driver includes a permanent magnet mounted on the scanning mechanism and a solenoid disposed opposite the permanent magnet. When energized, the solenoid produces a magnetic field varying periodically around the permanent magnet to swing the scanning mechanism.
The permanent magnet may also serve as the inertia body.
The permanent magnet has two magnetic poles arrayed perpendicular to the given swing line and is so located as to face a central portion of the permanent magnet when the scanning mechanism is at rest.
The driver may alternatively include a permanent magnet mounted on the scanning mechanism and two solenoids. The permanent magnet has magnetic poles arrayed parallel to the given swing line. The solenoid is disposed across one of the magnetic poles of the permanent magnet.
The driver may also have a magnetic field strength measuring device which measures a change in strength of a magnetic field of the permanent magnet caused by a swing of the scanning mechanism and outputs a signal indicative thereof.
The driver also includes a control circuit which is responsive to the signal outputted from the magnetic field strength measuring device to control energization of the solenoid so as to bring a swing of the scanning mechanism into a given condition.
The control circuit energizes the solenoid intermittently. The magnetic field strength measuring device uses the solenoid when deenergized to measure the change in strength of the magnetic field of the permanent magnet.
The driver may alternatively include piezoelectric devices adhered to the elastic plates which are so energized as to expand and contract the elastic plates in a cycle to swing the scanning mechanism.
The driver swings the scanning mechanism at a resonance frequency determined by mass of the scanning mechanism and spring constants of the elastic plates.
According to another aspect of the invention, there is provided a two-dimensional scanning device which comprises: (a) a first scanner directing a light beam emitted from a light source to a first scan direction; and (b) a second scanner directing the light beam inputted from the first scanner to a second scan direction traversing the first scan direction. Either or both of the first and second scanner include: (a) a housing; (b) a scanning mechanism constructed to be swingable about a given swing line to emit a light beam for scanning a given angular range, the scanning mechanism including a base and an inertia body projecting from the base toward the given swing line; (c) a support supporting the scanning mechanism on the housing so as to allow the scanning mechanism to swing, the support including a plurality of elastic plates each having a length one end of which is attached to the housing and other end of which is attached to the base of the scanning mechanism so that the elastic plates intersect each other with an offset on a line parallel to the given swing line, each of the elastic plates having a width in a direction parallel to the given swing line; and (d) a driver swinging the scanning mechanism to direct the light beam to the given angular range.
According to a further aspect of the invention, there is provided an optical scanner which comprises: (a) a housing including a pair of arms extending in the same direction; (b) a scanning mechanism constructed to be swingable about a given swing line to emit a light beam for scanning a given angular range; (c) a support supporting the scanning mechanism on the housing so as to allow the scanning mechanism to swing, the support including a pair of elastic plates surrounded by the arms of the housing, each of the elastic plates having a housing-attachment strip and a scanning mechanism-attachment strip, the housing-attachment strip having a bent end attached to an end of one of the arms of the housing, the scanning mechanism-attachment strip having a bent end attached to the scanning mechanism, the elastic plates being arranged adjacent each other so that ridges defined by bends of the ends of the housing-attachment strips and the scanning mechanism-attachment strips are arrayed along a line; and (d) a driver swinging the scanning mechanism about the line along which the ridges of the housing-attachment strips and the scanning mechanism-attachment strips are arrayed for directing the light beam to the given angular range.
In the preferred mode of the invention, the scanning mechanism has a reflecting surface for reflecting the light beam emitted from a light source toward the given angular range.
The center of gravity of the scanning mechanism is defined on the line along which the ridges of the housing-attachment strips and the scanning mechanism-attachment strips are arrayed.
The driver swings the scanning mechanism at a resonance frequency determined by mass of the scanning mechanism and spring constants of the elastic plates.
The driver includes a permanent magnet mounted on the scanning mechanism and a solenoid disposed opposite the permanent magnet. When energized, the solenoid produces an alternating field to move the permanent magnet, thereby swinging the scanning mechanism.
The permanent magnet is mounted on one of ends of the scanning mechanism opposed to each other in a direction of a swing of the scanning mechanism.
An inertia body may also be mounted on the other end of the scanning mechanism which adjusts the center of gravity of the scanning mechanism to a desired location.
Second inertia bodies may also be mounted on ends of the scanning mechanism opposed to each other in a direction parallel to the line about which the scanning mechanism swings.
The scanning mechanism has arms extending to a side of emission of the light beam to mount the second inertia bodies thereon.
Each of the elastic plates also has a second scanning mechanism-attachment strip. The housing-attachment strip is arranged between the scanning mechanism-attachment strip and the second scanning mechanism-attachment strip.
Each of the elastic plates has formed therein slits to define the housing-attachment strip and the scanning mechanism-attachment strips.
An end of each of the slits is rounded.
Each of the elastic plates may have a waved portion connecting between the housing-attachment strip and the scanning mechanism attachment strip.
Each of the elastic plates is made of a spring plate which has the housing-attachment strip formed on a first end thereof and the scanning mechanism-attachment strip formed on a second end opposite the first end and which is so deformed elastically that the ridges defined by the bends of the ends of the housing-attachment strips and the scanning mechanism-attachment strips are arrayed along the line about which the scanning mechanism swings.
The elastic plates are connected to each other to define a one-piece spring plate which has the housing-attachment strip and the scanning mechanism-attachment strip formed on each of opposed ends thereof.